Hollow cathode sputtering apparatus and related method

ABSTRACT

The present invention provides an improved hollow cathode method for sputter coating a substrate. The method of the invention comprises providing a channel for gas to flow through, the channel defined by a channel defining surface wherein one or more portions of the channel-defining surface include at least one target material. Gas is flowed through the channel wherein at least a portion of the gas is a non-laminarly flowing gas. While the gas is flowing through the channel a plasma is generated causing target material to be sputtered off the channel-defining surface to form a gaseous mixture containing target atoms that is transported to the substrate. In an important application of the present invention, a method for forming oxide films and in particular zinc oxide films is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. application Ser. No.10/635,344 filed Aug. 6, 2003. This application is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to methods and related apparatus fordepositing films on a substrate by hollow cathode sputtering. Moreparticularly, the present invention relates to methods and apparatus fordepositing oxide and other films by hollow cathode sputtering.

2. Background Art

Numerous methods are known for depositing thin films on a substrate.Such methods include, for example, sputtering, vacuum evaporation,chemical vapor deposition, and the like. Typical substrates that arecoated with thin films are glass, ceramics, and silicon wafers. Vacuumevaporation is a low pressure deposition technique in which a materialis vaporized by heating. Vacuum evaporation is a line of sightdeposition technique in which the vaporized material is then radiatedout in straight lines from the source. Chemical vapor deposition is athin film deposition technique in which a reactive gaseous mixture isheated over a substrate. The elevated temperature causes a chemicalreaction to occur from which a desired film is formed. Chemical vapordeposition can be undesirable because of contamination of the depositedfilms.

Sputtering is a low pressure deposition process in which a plasmacontaining gas ions and electrons is created by the action of anelectric field on gas that is introduced into a deposition chamber. Theelectric field may be formed by either a dc or rf voltage bias. Theseions are accelerated towards a target from which material is removed.This removed material is ultimately deposited on a nearby substrate.Reactive sputtering is a further refinement of the sputtering process inwhich a reactive gas such as nitrogen, oxygen, hydrogen, H₂O, H₂Se, CH₄,C₂H₆, C₂H₂, C₂H₄, B₂H₆, PH₃, CCl₄, CF₄, organic monomers like HMDSO,pyrrole and the like are introduced into the deposition chamber. Thesereactive gases are capable of reacting with the removed target materialto form a compound film on the substrate. Accordingly, these reactivegases provide one or more atoms that are incorporated into the film.Reactive sputtering is particularly useful for depositing doped andundoped metal oxides, nitrides, carbides, and the like. However, caremust be taken in the reactive sputtering process because such reactivegases may form an insulating layer on the conductive target therebyreducing film growth rate.

The effect of insulating layers on the targets in the sputtering processis generally alleviated by the use of RF power to form the plasma. Thistype of sputtering is referred to as RF sputtering. It is particularlyuseful for depositing both insulating and oxide films, but depositionrates tend to be low. In the RF sputtering process, a substrate isplaced between two electrodes which are driven by an RF power source.Superimposed on this applied RF field is a DC potential. This DCpotential advantageously drives the ions toward the target causing someof the target material to be removed. This removed target material maythen react with a reactive gas. Again the removed material ultimatelycoats the substrate.

A number of sputtering refinements makes this technique even moredesirable for the deposition of insulating and oxide films. Theserefinements include unbalanced magnetron sputtering, the utilization ofpulsed dc power, and the use of hollow cathodes. The utilization ofhollow cathode sputtering in a gas flow mode is a relatively newtechnique in which an inert gas such as argon is introduced into achannel in a target cathode. While contained within this channel aplasma is formed that removes atoms from the target. These atoms areeventually swept by the gas flow out of the cathode at which point theymay then be reacted with a reactive gas. The continuous flow of theinert gas prevents (or tends to prevent) the reactive gas from enteringthe cathode and thereby prevents (or tends to prevent) an insulatinglayer from forming on the target. Although the prior art hollow cathodeprocesses may inhibit the formation of an insulating layer on thetarget, these processes tend to produce films at unacceptably low growthrates.

Accordingly, there exists a need for improved sputtering methods fordepositing thin films and in particular insulating or oxide thin filmswith high growth rates and reduced formation of insulating layers on thetargets used in such sputtering processes.

SUMMARY OF THE INVENTION

The present invention overcomes the problems of the prior art byproviding in one embodiment an improved method for sputter coating asubstrate. The method of the invention is a hollow cathode sputteringprocess which comprises providing a channel for gas to flow through, thechannel defined by a channel defining surface wherein one or moreportions of the channel-defining surface includes at least one targetmaterial. Gas is flowed through the channel wherein at least a portionof the gas is a non-laminarly flowing gas. While the gas is flowingthrough the channel a plasma is generated causing target material to besputtered off the channel-defining surface to form a gaseous mixturecontaining target atoms that are transported to the substrate. In animportant application of the present invention, a method for formingoxide films and in particular zinc oxide films is provided.

In another embodiment of the present invention, a sputter-coating systemfor coating a substrate is provided. Such a sputter-coating system willinclude at least one target material, an electrode having achannel-defining surface, and a source of non-laminarly flowing workinggas. The channel-defining surface contains the target material. Duringoperation of the sputter-coating system, a plasma is generated causingthe at least one target material to be sputtered off thechannel-defining surface. This in turn causes a gaseous reactivecomposition to form which is subsequently transported to the substrate.

The source of non-laminarly flowing gas includes a series of orificessuch that at least two gas streams emerging from the series of orificesare substantially flowing in non-parallel directions. The source ofnon-laminarly flowing gas includes a series of adjacent orifices thatdirect the gas in non-parallel directions. The channel defining surfacewill typically be part of the cathode. Moreover, the channel ischaracterized by a generally rectangular cross section. Thesputter-coating system may have a first target material and a secondtarget material. The first target material is preferably opposite thesecond where the first target material and the second target materialare the same or different. In such a configuration, the two targetmaterials will form at least a portion of the side walls of thechannel-defining surface, and in particular the side walls that make upthe wider sides when the channel has a rectangular cross section.Moreover, the at least one target material optionally includes a thirdtarget material and a fourth target material. The third target materialbeing opposite the fourth target material. In this instance, the firsttarget material, the second target material, the third target material,and the fourth target material may be the same or different. The targetmaterial, which is typically part of the cathode, is in electricalcontact with a DC potential or a DC potential with a superimposed ACpotential. Moreover, the at least one target material comprises a metalor metal alloy. Suitable target materials include, but are not limitedto, zinc, copper, aluminum, silicon, tin, indium, magnesium, titanium,chromium, molybdenum, nickel, yttrium, zirconium, niobium, cadmium, andmixtures thereof. The sputter-coating system of the present inventionfurther comprises a source of a reactive gas which is located atproximate position to the exit of the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic demonstrating laminar gas flow in a hollowcathode with a baffle between the gas nozzle and the channel defined bythe target materials;

FIG. 1B is a schematic demonstrating laminar gas flow in a hollowcathode with the gas nozzle between the baffle and the channel definedby the target materials;

FIG. 1C is a schematic demonstrating the utilization of non-laminar gasflow in a hollow cathode by creating a narrow passage between the gasnozzle and the target materials;

FIG. 1D is a schematic demonstrating the utilization of non-laminar gasflow in a hollow cathode by directing the gas flow into non-paralleldirections;

FIG. 2 is a perspective view of a gas nozzle which introduces a gas withnon-parallel directions into the channel.

FIG. 3 is a plot of a waveform that may be used to drive a sputteringsystem with an asymmetric bipolar pulsed DC power supply.

FIG. 4A is a perspective view of a target that is capable of holding uptwo target materials separated by two insulating blocks;

FIG. 4B is a front view of a target that is capable of holding up twotarget materials separated by two insulating blocks;

FIG. 4C is a perspective view of a target that is capable of holding upfour target materials;

FIG. 4D is a perspective view of a target that is capable of holding upfour target materials;

FIG. 5A is a schematic of an embodiment of the sputter-coating system ofthe present invention;

FIG. 5B is a schematic of the cathode used in the sputter-coating systemof the present invention;

FIG. 6 is a plot of the deposition rate as a function of oxygen flowrate for aluminum oxide films deposited from an aluminum target by themethod of the present invention operating with a power of 300 W, apressure of 250 mTorr, and an argon flow rate of 4 slm for the cases ofoxygen injection outside the cathode and oxygen passing through thecathode;

FIG. 7 is a plot of zinc oxide growth rate as a function of the argonflow rate for zinc oxide films deposited from a zinc target by themethod of the invention operating with power of 150 W, a pressure of 500mTorr, and an oxygen flow rate of 150 sccm; and

FIG. 8 is a plot of the deposition rate of aluminum oxide films as afunction of oxygen flow rate for non-laminar and laminar flow by themethod of the present invention operating at a power of 300 W, apressure of 500 mTorr, and argon flow rates of 2 slm and 4 slm. Theoxygen is injected outside the cathode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Reference will now be made in detail to presently preferred compositionsor embodiments and methods of the invention, which constitute the bestmodes of practicing the invention presently known to the inventors.

In one embodiment of the present invention, a method for sputter coatinga substrate utilizing a hollow cathode in a sputter coating reactor isprovided. The method of the invention comprises providing a channel(i.e., a cathode channel) for gas to flow through, the channel definedby a channel defining surface wherein one or more portions of thechannel-defining surface include at least one target material.Typically, the channel defining surface is part of the cathode of asputtering system and has a rectangular cross section. Gas is flowedthrough the channel wherein at least a portion of the gas is anon-laminarly flowing gas. Preferably, this gas will be an inert gassuch as argon. Such inert gases are sometimes referred to as workinggases in that these gases are used to sputter off material from targetsurfaces. FIGS. 1 A through D are schematics illustrating laminar flowand the methods of the present invention. With reference to FIGS. 1 Aand B, gas is introduced from nozzle 2 into channel 4. Prior to enteringchannel 4, the gas impinges on baffle 6 which helps in mixing. While thegas is flowing through channel 4 a plasma is generated causing targetmaterial to be sputtered off the channel-defining surface 8 to form agaseous mixture containing target atoms that are transported tosubstrate 10. With reference to FIG. 1C, a configuration suitable forsmall gap cathodes is provided. In this configuration, non-laminar flowis induced by placing nozzle 2 within channel 4. This causes gas thatimpinges on baffle 6 to be forced at a relatively higher velocitythrough narrow passage 12 which is formed between nozzle 2 andchannel-defining surfaces 8. The higher velocity gas flow close to thetarget surface is maintained across the length of the channel fromentrance to exit or across at least part of the channel. With referenceto FIG. 1D, a configuration that is suitable for large gap cathodes isprovided. In this configuration, nozzle 2 is placed in channel 4. Gasemerging from nozzle 2 is forced to flow through flow directing shield14 which directs the gas in a number of non-parallel directions. It willbe appreciated that the flow directing properties of shield 14 may bebuilt directly into nozzle 2 by having orifices in nozzle 2 that directthe gas in non-parallel directions. The requirement that the gas beflowing non-laminarly is important in achieving the advantages of thepresent invention. A preferred way to achieve non-laminar flow is byinducing turbulence. Typically, turbulent flow is characterized ashaving a Reynolds number greater than 2000. A slightly differentpreferred way of achieving non-laminar flow is by having differentportions of the gas flow in different directions. In its simplestembodiment of this concept, a first portion of gas in a first directionand a second portion of gas is a second direction wherein the firstdirection and the second direction are substantially non-parallel. Withreference to FIG. 2 a perspective view of gas nozzle 13 which introducesa gas into the channel is provided. Typically, the gas will beintroduced into a sputtering reactor through a manifold 15 with a seriesof orifices 16 from which the gas emerges. Accordingly, thenon-laminarly flowing gas is formed by flowing the gas through at leasttwo orifices such that at least two gas streams emerging from the atleast two orifices are flowing in substantially non-parallel directions.In practice, however, the manifold will contain numerous orificeswherein two adjacent orifices will direct the gas flow in differentnon-parallel directions.

The target material, which is typically part of the cathode, is inelectrical contact with a DC potential, a DC potential with asuperimposed AC potential, or a pulsed DC potential. The preferred powersource is a pulsed DC power source and in particular an asymmetricbipolar pulsed DC power supply. An asymmetric bipolar power is appliedbetween the cathode and anode by adding a reverse (opposite polarity)voltage pulse to the normal (steady negative) DC waveform. The resultingwaveform is shown in FIG. 3. Typical sputtering runs at about −400V, sothat the positive argon ions accelerate towards the target biased at−400V, striking and sputtering the target (sputtering mode). However, inreactive sputtering, reaction of the gas (oxygen, for example) with thetarget material can create an insulating film on the target surface.Positive charge from the ions builds up on the film surface and reducesthe incoming ion energy because of electrostatic repulsion. This makesit difficult or impossible to remove the oxide since sputtering iseffectively prevented. If DC sputtering is attempted, the presence of aninsulator on the target surface leads to arcing. Using the bipolar typeof supply described above, when the polarity is rapidly reversed toabout +100V, the surface charges up to −100V because of the attractionof electrons. Next, upon returning to sputtering mode, −400V is appliedto the target and the effective voltage on the surface of the oxide is−500V. Thus, the argon ions are drawn by electrostatic attraction to theinsulators, and strike with extra energy. This helps sputter off theinsulators, reducing target poisoning. The frequency normally used isfrom 50 kHz to 250 kHz. The reverse pulse width can be set anywherebetween 0 and 40% of the pulse's duty cycle. Depending on the targetmaterial and the rate of oxide formation, the use of asymetric bipolarpulsed power may only have limited effectiveness in removal ofinsulating layers. Even with the flow of inert gas through the cathode(laminar or non-laminar), some backstreaming of the reactive gas(oxygen, say) may occur and partially oxidize the target surface.Asymmetric bipolar pulsed DC supplies usually have low energy storagewhich also reduces arcing. A similar benefit occurs when a new target isbeing run for the first time (burn-in). The time required to stabilizethe discharge is decreased, resulting in faster burn-in. Depending onthe power supply manufacturer, the pulse shape may not be rectangular.This does not affect the principles described.

The at least one target material used in the method of the inventioncomprises a metal or metal alloy. Suitable target materials include, butare not limited to, zinc, copper, aluminum, silicon, tin, indium,magnesium, titanium, chromium, molybdenum, nickel, yttrium, zirconium,niobium, cadmium, and mixtures thereof.

In a preferred variation of the present invention, the target materialincludes a first target material and a second target material. The firsttarget material is preferably opposite the second where the first targetmaterial and the second target material are the same or different. Insuch a configuration, the two target materials will form at least aportion of the side walls of the channel-defining surface, and inparticular the side walls that make up the wider sides when the channelhas a rectangular cross section. Moreover, the at least one targetmaterial optionally includes a third target material and a fourth targetmaterial. The third target material being opposite the fourth targetmaterial. In this instance, the first target material, the second targetmaterial, the third target material, and the fourth target material maybe the same or different.

FIGS. 4A through D provide schematics of a water-cooled Cu cathodefitted with four target pieces (two large side pieces and two smallerend blocks). With reference to FIGS. 4A and 4B, a perspective view and afront view of a target that is capable of holding up to two targetmaterials separated by insulating blocks is provided. Target 20 consistsof plate 22 and plate 24 with are opposite and face each other. Plate 22is made from the first target material and plate 24 is made of thesecond target material. Target 20 also consists of insulating blocks 26,28 which are opposite and face each other. Insulating end blocks 26, 28are made from an electrically insulating material such as Macor (amachinable ceramic from Corning). Insulating end blocks 26, 28 areisolated from plates 22, 24 by gaps 30, 32, 34, 36. The gap width foreach of gaps 30, 32, 34, 36 is about 0.5 mm to 1.0 mm. Without suchgaps, the arcs result from a potential difference between the floatingmetal film that builds up on the insulator surface during the sputteringprocess and the target proper. This metal film builds up on theinsulator close to the target until a discharge occurs. Once thedischarge occurs, arcs continue until the metal film near the target isburned away. This arc-generating process then repeats during thin filmdeposition. With appropriate sizing of the insulators and target piecesto create a gap, a discharge between the target and a metal film on theinsulator cannot occur because of the gap spacing. The insulating endblocks make the film thickness distribution in the direction of the longaxis of the slot more uniform than if additionally metal targets areplaced there. If a back insulator (not shown) is used on the rear of thecathode for construction purposes, a similar principle is used to createa gap between the back insulator and the target pieces. Without theceramic end blocks, the thickness distribution strongly peaks near thetwo ends of the slot. Plates 22, 24 are contained within cooling jacket38 through which a coolant such as water flows to keep the targetmaterials cooled. This figure shows the water-cooled Cu cathode fittedwith four target pieces (two large side pieces and two smaller endblocks). The exit slot defined by the inner surfaces of the targetpieces is evident. When all four target pieces are metals, they may buttup against each other as shown.

With reference to FIGS. 4C and 4D, a perspective view and a front viewof a target that is capable of holding up to four target materials areprovided. Target 40 consists of wide plate 42 and wide plate 44 whichare opposite and face each other. Wide plate 42 is made from the firsttarget material and wide plate 44 is made of the second target material.Target 40 also consists of short plate 46 and short plate 48 which areopposite and face each other. Short plate 46 is optionally made from thethird target material and short plate 48 is optionally made from thefourth target material. Plates 42, 44, 46, 48 are contained withincooling jacket 50 through which a coolant such as water flows to keepthe target materials cooled.

The method of the present invention optionally further includes a stepof introducing a reactive gas into the sputter coating reactor. Thereactive gas is introduced into the sputter coating reactor at aposition located outside of the channel from which the gaseous mixtureemerges prior to reaching the substrate. The reactive gas contains anatom selected from the group consisting of oxygen, nitrogen, selenium,sulfur, iodine, hydrogen, carbon, boron, and phosphorus. Suitablereactive gases include, but are not limited to, molecular oxygen,molecular nitrogen, molecular hydrogen, H₂O, H₂Se, CH₄, C₂H₆, C₂H₂,C₂H₄, B₂H₆, PH₃, CCl₄, CF₄, HMDSO, pyrrole and mixture thereof.

In a particularly useful application of the method of the presentinvention, a method for depositing an oxide film on a substrate in asputter coating reactor is provided. This oxide forming method comprisesthe following steps:

a) providing a channel for a working gas to flow through, the channeldefined by a channel-defining surface wherein one or more portions ofthe channel-defining surface include at least one target material;

b) flowing the working gas through the channel wherein at least aportion of the working gas flows non-laminarly;

c) generating a plasma wherein a portion of the target material issputtered off the at least one target material to form a gaseous mixturecontaining target atoms; and

d) introducing into the sputter coating reactor a reactive gas thatcomprises oxygen, wherein an oxide film is deposited on the substrate.Preferably, the working gas is an inert gas such as argon. The reactivegas is introduced at a position located outside of the channel fromwhich the gaseous mixture emerges prior to reaching the substrate. Theat least one target material comprises a metal, metal alloy, or asemiconductor. Examples of useful target materials include, but are notlimited to, zinc, copper, aluminum, silicon, tin, indium, magnesium,titanium, chromium, molybdenum, nickel, yttrium, zirconium, niobium,cadmium, and mixtures thereof. Preferred oxide films made by the methodinclude zinc oxide made by using a target which includes zinc and CrSiOxmade from a target that includes both chromium and silicon, wherein x isa number such that the valency of Cr and Si are satisfied or partiallysatisfied. Transparent electrically conducting oxides that may be madeby the method of the present invention include, for example, ZnO:B(boron doped zinc oxide), CuAlO₂, CuBO₂, In₂O₃, In₂O₃:Mo (molybdenumdoped indium oxide), ITO (indium tin oxide), Al₂O₃, or mixtures thereof.In the case of zinc oxide, the target may also include aluminum so thatan aluminum doped zinc oxide film (ZnO:Al) is formed. Gallium and indiumare also suitable dopants for zinc oxide. In the case of ZnO:B, thesource of the boron atoms is conveniently the gas diborane (B₂H₆). Thediborane may be introduced either externally or internally to thecathode. External introduction avoids target memory effects, and ispreferred. In the case of CuBO₂, the boron is preferably introduced byflowing a mixture of the working gas and diborane through the cathode.Magnesium oxide and aluminum oxide, which are highly insulating films,may be advantageously made by the method of the invention. In formingoxide films, the reactive gas must necessarily include compounds thathave an oxygen atom. Useful examples of such gases include, but are notlimited to, molecular oxygen and H₂O. The present variation of themethod of the invention may include a first, second, third, and fourthtarget material as set forth above.

In another embodiment of the present invention, a method for depositinga nitride film on a substrate in a sputter coating reactor is provided.The method of this embodiment comprises providing a channel for aworking gas to flow through, the channel defined by a channel-definingsurface wherein one or more portions of the channel-defining surfaceinclude at least one target material. The working gas is then flowedthrough the channel wherein at least a portion of the working gas flowsnon-laminarly. While the working gas is flowing, a plasma is generatedwherein a portion of the target material is sputtered off the at leastone target material to form a gaseous mixture containing target atoms.Finally, a reactive gas comprising molecular nitrogen is introduced intothe sputter coating reactor, wherein a nitride film is deposited on thesubstrate. In one variation of this embodiment the reactive gas isintroduced at a position located outside of the channel from which thegaseous mixture emerges. In a particularly preferred variation of thisembodiment, the reactive gas is combined with the working gas (e.g. Ar)while it is flowed through the channel (i.e., the cathode channel.) Theneed to mix the reactive gas and the working gas in the cathode channelis likely due to the lower reactivity of nitrogen gas compared tooxygen. The success may relate to the relatively high electricalconductivity of many metal nitrides. The configuration of the at leastone target material is the same as set forth above. For example, the atleast one target material includes a first target material and a secondtarget material; and the first target material and the second targetmaterial are the same or different. In this configuration, the firsttarget material is preferably opposite the second target material.Moreover, the at least one target material typically comprises a metal,metal alloy, or semiconductor. Preferably, the at least one targetmaterial comprises a component selected from the group consisting ofzinc, copper, aluminum, silicon, tin, indium, magnesium, titanium,chromium, molybdenum, nickel, yttrium, zirconium, niobium, cadmium,vanadium, hafnium, tungsten, and mixtures thereof. Examples of nitridesthat may be made by the method of this embodiment include titaniumnitride, indium nitride, aluminum nitride, chromium nitride, vanadiumnitride, tungsten nitride, copper nitride, zirconium nitride, ormixtures thereof.

With reference to FIG. 5A a schematic of the sputter-coating system ofthe present invention is provided. Sputter system 60 includes cathode 62into which a non reactive gas such as argon is introduced into injector64 by tube 66. Cathode 62 is powered by high voltage power supply 68.Within cathode 62 a gaseous mixture containing target atoms as set forthabove is formed and transported toward substrate 70. Upon emerging fromcathode 62, the gaseous mixture combines with a reactive gas that isintroduced from manifold 72. Low pressure is maintained within chamber74 by the operation of throttle valve 76 and pumping system 78.Moreover, substrate 70 is heated by heating lamps 80 and transportedthrough the sputtering system by transport mechanism 82. With referenceto FIG. 5B, a schematic cross-section of cathode 62 is provided. Cathode62 includes targets 90, 92 which are made of materials as set forthabove. Targets 90,92 are powered through electrical feed 94. Cathode 62is cooled via copper cooling block 96 which is water cooled. Water isintroduced into copper cooling block 96 through teflon tube 98 whichsnakes through leak tight adapter 100. Teflon tube 98 attaches to coppercooling block 96 via connector 102. Similarly, water is removed fromcopper cooling block 96 through teflon tube 104 which snakes throughleak tight adapter 106. Teflon tube 104 attaches to copper cooling block96 via connector 110. Back section 112 is electrically isolated fromcooling section 96 and targets 90, 92 by ceramic insulators 114, 116.Cathode 62 also includes dark shield 118 and ceramic support 120 whichholds cathode 62 in place. A non-reactive gas such as argon isintroduced into the cathode by inlet 122. The gas then emerges fromnozzle 124. Next the gas is redirected by flow directing shield 126which causes the gas to flow in non-parallel directions. The gas enterschannel 128 wherein a plasma is generated and material is sputtered offof targets 90, 92. The resulting gaseous mixture includes targetmaterial atoms which are transported to the substrate. Reactive gasmanifold 130 is positioned near the exit of channel 128. Reactive gasmanifold 130 introduces a reactive gas that mixes with the gaseousmixture that includes the target atoms.

As set forth for the method described above, the source of non-laminarlyflowing gas includes a series of orifices such that at least two gasstreams emerging from the series of orifices are substantially flowingin non-parallel directions. The source of non-laminarly flowing gasincludes a series of adjacent orifices that direct the gas innon-parallel directions. The channel defining surface will typically bepart of the cathode. Moreover, the channel is characterized by arectangular cross section. Again, as described above for the method, thesputter-coating system may have a first target material and a secondtarget material. The first target material is preferably opposite thesecond where the first target material and the second target materialare the same or different. In such a configuration, the two targetmaterials will form at least a portion of the side walls of thechannel-defining surface, and in particular the side walls that make upthe wider sides when the channel has a rectangular cross section.Moreover, the at least one target material optionally includes a thirdtarget material and a fourth target material. The third target materialbeing opposite the fourth target material. In this instance, the firsttarget material, the second target material, the third target material,and the fourth target material may be the same or different. The targetmaterial, which is typically part of the cathode, is in electricalcontact with a DC potential or a DC potential with a superimposed ACpotential. Moreover, the at least one target material comprises a metalor metal alloy. Suitable target materials include, but are not limitedto, zinc, copper, aluminum, silicon, tin, indium, magnesium, titanium,chromium, molybdenum, nickel, yttrium, zirconium, niobium, cadmium, andmixtures thereof. The sputter-coating system of the present inventionfurther comprises a source of a reactive gas which is located atproximate position to the exit of the channel.

The following examples illustrate the various embodiments of the presentinvention. Those skilled in the art will recognize many variations thatare within the spirit of the present invention and scope of the claims.

EXAMPLE 1

Copper films were deposited in accordance to the method of the presentinvention at a power of 1000 W, a pressure of 400 mTorr, and an argonflow rate of 4 slm. The resistivities for a series of copper films forvarying substrate conditions is provided in Table 1. TABLE 1 Resistivityof copper films film resistivity deposition conditions (microhm cm)unheated substrate 8.5 bias −30 V, unheated substrate 4.2 bias −15 V,substrate 70° C. 3.9 substrate heated to 70° C. 3.3 bias −30 V,substrate 70° C. 2.4

EXAMPLE 2

Aluminum oxide films were deposited by the method of the invention witha power of 300 W, a pressure of 250 mTorr, and an argon flow rate of 4slm. The argon was injected using the arrangement of FIG. 1C. FIG. 6 isa plot of the deposition rate as a function of oxygen flow rate. Thereactive gas O₂ is used here for two different cases: O₂ goes throughthe channel and O₂ is outside the channel. The deposition rate wasmeasured by crystal monitor.

EXAMPLE 3

Zinc oxide films were deposited by the method of the invention withpower of 150 W, a pressure of 500 mTorr, and an oxygen flow rate of 150sccm. FIG. 7 is a plot of zinc oxide growth rate as a function of theargon flow rate for deposition in a hollow cathode reactor where theargon is introduced non-turbulently and turbulently. In the case ofturbulent flow, the film growth rate is observed to be significantlygreater for all argon flow rates.

EXAMPLE 4

Aluminum doped zinc oxide films were deposited by the method of theinvention with the conditions in Table 2. Table 3 provides a comparisonfor aluminum doped zinc oxide films made by the method of the presentinvention and by RF sputtering. Table 3 demonstrates that the method ofthe present invention is capable of depositing doped zinc oxide filmswith resistivities that are comparable to RF sputtering. TABLE 2Aluminum doped zinc oxide deposition conditions. target- oxygensubstrate resistivity Power Pressure flow rate distance (10⁻³ ohm- Run(W) (mTorr) (sccm) (cm) cm) 1 100 300 70 2.0 0.49 2 100 200 70 3.5 1.263 100 200 100 3.5 0.49 4 100 200 500 3.5 48 5 100 200 140 3.5 1.5 6 100100 150 5.5 5.9 7 100 100 250 5.5 large 8 250 300 100 2.5 1.2

TABLE 3 Aluminum doped zinc oxide properties. sheet resistance thicknessresistivity Run method (Ω/□) (μm) (10⁻³ Ω-cm) 1 hollow cathode 13 0.380.49 2 hollow cathode 23 0.52 1.19 3 hollow cathode 14 0.9 1.26 4 RFmagnetron 5 0.89 0.45 5 RF magnetron 16 0.43 0.69 6 RF magnetron 14 0.630.88

EXAMPLE 5

Aluminum and aluminum oxide films were deposited by the method of theinvention with a power of 300 W, a pressure of 500 mTorr, and argon flowrates of 2 slm and 4 slm. FIG. 8 is a plot of the aluminum oxidedeposition rate as a function of oxygen flow rate for turbulent andnon-turbulent Ar flow. For non-laminar flow, the gas injector is thetype in FIG. 1C and for non-turbulent flow, the gas injector is the typeof FIG. 1A. Again, the growth rates for all oxygen flow rates isobserved to be significantly higher with turbulent Ar flow. Even forzero oxygen flow, the deposition rate of pure Al is enhanced byturbulent flow. With the addition of oxygen, the deposited mass rateincreases because of oxygen incorporation into the film. The mass ratesaturates once a fully oxidized film is formed. The increase indeposition rate with turbulence is even greater for aluminum oxide thanfor pure aluminum. This rate enhancement is of considerabletechnological importance. At the lower Ar flow (2 slm) the depositionrate without turbulent Ar flow is seen to decline with increasing oxygenflow. This is believed to result from partial penetration of oxygen intothe cathode, resulting in partial oxidation of the target surface. Withturbulent Ar flow, the deposition rate is independent of oxygen flow.This suggests that turbulence, as well as increasing the mass of Al thatcan be moved out of the cathode, also hinders the back-diffusion ofoxygen into the cathode.

EXAMPLE 6

The transparent conductor ZnO:B was deposited by the method of theinvention using zinc target pieces, turbulent Ar gas injection (type(c)), an Ar gas flow rate of 2 slm, a power of 300 W, a pressure of 300mTorr, 120 sccm O₂ supplied from a manifold external to the cathode anddirected at the substrate, and 2 sccm B₂H₆ gas passing through thecathode and mixed with the Ar. The deposition rate was 20 A/s and thefilm resistivity was 1.8×10³ ohm cm.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A method for sputter coating a substrate in a sputter coatingreactor, the method comprising: a) providing a channel for gas to flowthrough, the channel defined by a channel defining surface wherein oneor more portions of the channel-defining surface include at least onetarget material; b) flowing gas through the channel wherein at least aportion of the gas is a non-laminarly flowing gas; and c) generating aplasma, wherein the target material is sputtered off thechannel-defining surface to form a gaseous mixture containing targetatoms that is transported to the substrate.
 2. The method of claim 1wherein the non-laminarly flowing gas is formed by turbulence.
 3. Themethod of claim 1 wherein the non-laminarly flowing gas is formed byflowing a first portion of gas in a first direction and a second portionof gas in a second direction wherein the first direction and the seconddirection are substantially non-parallel.
 4. The method of claim 1wherein the non-laminarly flowing gas is formed by flowing the gasthrough at least two orifices such that at least two gas streamsemerging from the at least two orifices are flowing in substantiallynon-parallel directions.
 5. The method of claim 1 wherein thenon-laminarly flowing gas is formed flowing the gas through a series oforifices such that adjacent orifices direct the gas in non-paralleldirections.
 6. The method of claim 1 wherein the non-laminarly flowinggas is formed by turbulence with a Reynolds number greater than
 2000. 7.The method of claim 1 wherein the channel-defining surface is part of acathode.
 8. The method of claim 1 wherein the channel has a rectangularcross section.
 9. The method of claim 1 wherein the target material isin electrical contact with a DC potential, a DC potential with asuperimposed AC potential, or a pulsed DC potential.
 10. The method ofclaim 1 wherein the target material is in electrical contact with apulsed DC power source that is an asymmetric bipolar pulsed DC powersupply.
 11. The method of claim 1 wherein the at least one targetmaterial comprises a metal or metal alloy.
 12. The method of claim 1wherein the at least one target material comprises a component selectedfrom the group consisting of zinc, copper, aluminum, silicon, tin,indium, magnesium, titanium, chromium, molybdenum, nickel, yttrium,zirconium, niobium, cadmium, and mixtures thereof.
 13. The method ofclaim 1 wherein the at least one target material includes a first targetmaterial and a second target material, the first target material beingopposite the second and wherein the first target material and the secondtarget material are the same or different.
 14. The method of claim 13wherein the first target material and the second target materialcomprise a metal or a metal alloy.
 15. The method of claim 13 whereinthe first target material and the second target material independentlyinclude a component selected from the group consisting of zinc, copper,aluminum, silicon, tin, indium, magnesium, titanium, chromium,molybdenum, nickel, yttrium, zirconium, niobium, cadmium, and mixturesthereof.
 16. The method of claim 13 wherein the at least one targetmaterial includes a third target material and a fourth target material,the third target material being opposite the fourth target material andwherein the first target material, the second target material, the thirdtarget material, and the fourth target material are the same ordifferent.
 17. The method of claim 13 wherein the at least one targetmaterial includes a first electrically insulating block and a secondelectrically insulating block, the first insulating block being oppositethe second insulating.
 18. The method of claim 13 further comprisingintroducing a reactive gas into the sputter coating reactor.
 19. Themethod of claim 18 wherein the reactive gas is introduced at a positionlocated outside of the channel from which the gaseous mixture emerges.20. The method of claim 18 wherein the reactive gas contains an atomselected from the group consisting of oxygen, nitrogen, selenium,sulfur, iodine, hydrogen, carbon, boron, and phosphorus.